Next we turn to the temporal evolution in the resonance line profiles
shown in Fig. REF . In 2007 the Ca i and Li i lines both displayed pure P Cygni profiles, while a splitting
into two absorption components becomes evident for our data from 2011 on. According to the analysis
by [1]}, the bluer of these absorption components is formed in the matter
ejected in 2002 and presumably represents a fast moving shell. A comparison of the strengths of
the shell absorption components in both Ca i and Li i implies that the opacity in the
Li line is higher than in the Ca line. Because the opacity drops with the drop in density of the
expanding shell material, which for an assumed constant expansion velocity becomes proportional to
\(r^{-2}\)  where \(r\)  is the distance from the star, the weakening of the less opaque shell component in
Ca and its slightly smaller blue-shifted velocity compared to Li is evidence for a density and
velocity gradient within the expanding shell. In contrast, the redder of the two absorption components
is similar in both lines and is formed most probably in the ongoing wind of V838 Mon. The existence
of such a wind is evident from the representative P Cygni-type profiles of the persistent K i
7698 Å resonance line presented in [2]} and
[3]} over the years 2002–2020. This potassium
line is a good example to demonstrate that even at epochs when the Ca i and Li i
resonance lines suggest a weakening of the wind (see Fig. REF ), the high ground-level
population of K i still results in saturated wind profiles over all Doppler velocities
[3]}. A similar saturation was present in Ca i and
Li i in 2007.
